The present invention relates to an improvement in a diesel engine glow plug having a ceramic heater made of a resistive ceramic material.
Generally, since a diesel engine has poor starting characteristics, a glow plug is disposed in a subcombustion chamber or a combustion chamber. In this case, a current is flowed through the glow plug so that the glow plug generates heat. Thus, the glow plug is used to increase an intake air temperature or used as an ignition source, thereby improving the starting characteristics of the engine.
In recent years, as a glow plug of this type, a ceramic heater type glow plug has received a great deal of attention since it is superior in heating characteristics and the like to a conventional sheath type glow plug. Conventional ceramic heaters are a heater obtained by embedding a metal heating wire in an insulating ceramic material as disclosed in Japanese patent laid-open (Kokai) no. 57-41523 and a heater obtained by forming a heating member made of a resistive ceramic material integrally with an insulating ceramic material as disclosed in Japanese patent laid-open (Kokai) Nos. 60-9085 and 60-14784.
In such a conventional ceramic heater type glow plug, the ceramic heater described above is generally bonded and fixed to the distal end portion of a holder as a glow plug main body by brazing or the like. One end of a metal conductive wire is connected to a heater rear end portion by welding or the like and the other end of the wire is connected to an external connecting terminal held at the holder rear end portion through an insulating bush and the like. Thus, the heater and the holder are assembled integrally with each other.
However, the above conventional ceramic heater type glow plug has three bonded portions, i.e., a brazed portion between the heater and the holder and welded portions at the both ends of the metal conductive wire, resulting in troublesome and cumbersome assembly and high cost. Moreover, peeling or the like of the brazed portion or the welded portion poses a problem. This problem is significant at the bonded portion between the heater made of a ceramic material and the holder made of a metal material. Thus, the above conventional glow plug poses a problem in assuring operational reliability. Therefore, demand has arisen for a countermeasure capable of solving the above problems.